an introduction to rigid pavement design

8/12/2019 An Introduction to Rigid Pavement Design

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An Introduction to Rigid Pavement Design 1. INTRODUCTION This is an introduction to rigid pavement design for engineers. It is not intended as definitive treatise,

and it does not encompass the design of flexible pavements.Engineers are cautioned that much of

pavement design is governed by codes, specifications and practices of public agencies. Engineers must

always determine the requirements of the regulatory authority within whose jurisdiction specific

projects fall.

2. RIGID PAVEMENT DESIGN

2.1 Soil Classification and Tests

All soils should be classified according to the Unified Soil Classification System (USGS) as given in

ASTM D 2487. There have been instances in construction specifications where the use of such terms

as "loam," gumbo, "mud," and "muck" have resulted in misunderstandings. These terms are not

specific and are subject to different interpretations throughout the United States. Such terms shouldnot be used. Sufficient investigations should be performed at the proposed site to facilitate the

description of all soils that will be used or removed during construction in accordance with ASTM D

2487; any additional descriptive information considered pertinent should also be included. If Atterberg

limits are a required part of the description, as indicated by the classification tests, the test procedures

and limits should be referenced in the construction specifications.

2.2 Compaction

2.2.1General

Table 2-1Modulus of Soil Reaction
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Figure 2-1Effect of Base-Course Thickness on Modulus of Soil Reaction

Compaction improves the stability of the subgrade soils and provides a more uniform foundation for

the pavement. ASTM D 1557 soil compaction test conducted at several moisture contents is used to

determine the compaction characteristics of the subgrade soils. This test method should not be used if

the soil contains particles that are easily broken under the blow of the tamper unless the field method

of compaction will produce a similar degradation. Certain types of soil may require the use of a

laboratory compaction control test other than the above-mentioned compaction test. The unit weight

of some types of sands and gravels obtained using the compaction method above may be lower than

the unit weight that can be obtained by field compaction; hence, the method may not be applicable. In

those cases where a higher laboratory density is desired, compaction tests are usually made under

some variation of the ASTM D 1557 method, such as vibration or tamping (alone or in combination)

with a type hammer or compaction effort different from that used in the test.

2.2.2 Requirements For all subgrade soil types, the subgrade under the pavement slab or base course must be compacted

to a minimum depth of 6 inches. If the densities of the natural subgrade materials are equal to or

greater than 90 percent of the maximum density from ASTM D 1557, no rolling is necessary other

than that required to provide a smooth surface. Compaction requirements for cohesive soils (LL > 25;

PI > 5) will be 90 percent of maximum density for the top 6 inches of cuts and the full depth of fills.

Compaction requirements for cohesionless soils (LL < 25: PI


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2.2.3 Special Soils Although compaction increases the stability and strength of most soils, some soil types show a marked

decrease in stability when scarified, worked, and rolled. Also, expansive soils shrink excessively during

dry periods and expand excessively when allowed to absorb moisture. When any of these types are

encountered, special treatment will be required. For nominally expansive soils, water content,

compaction effort, and overburden should be determined to control swell. For highly expansive soils,

replacement to depth of moisture equilibrium, raising grade, lime stabilization, prewetting, or other

acceptable means of controlling swell should be considered.

2.3 Treatment of Unsuitable Soils Soils not suitable for subgrade use should be removed and replaced or covered with soils which are

suitable. The depth to which such adverse soils should be removed or covered depends on the soil

type, drainage conditions, and depth of freezing temperature penetration and should be determined

by the engineer on the basis of judgment and previous experience, with due consideration of the

traffic to be served and the costs involved. Where freezing temperatures penetrate a frost-susceptible

subgrade, special design procedures should be followed.

In some instances, unsuitable or adverse soils may be improved economically by stabilization with

such materials as cement, flyash, lime, or certain chemical additives, whereby the characteristics of

the composite material become suitable for subgrade purposes. However, subgrade stabilization

should not be attempted unless the costs reflect corresponding savings in base-course, pavement, or

drainage facilities construction.

2.4 Determination of Modulus of SubgradeReaction For the design of rigid pavements in those areas where no previous experience regarding pavement

performance is available, the modulus of subgrade reaction k to be used for design purposes is

determined by the field plate-bearing test. This test procedure and the method for evaluating its

results are not part of this discussion. Where performance data from existing rigid pavements are

available, adequate values for k can usually be determined on the basis of consideration of soil type,

drainage conditions, and frost conditions that prevail at the proposed site. Table 2-1 presents typical

values of k for various soil types and moisture conditions. These values should be considered as a

guide only, and their use in lieu of the field plate-bearing test, although not recommended, is left to

the discretion of the engineer. Where a base course is used under the pavement, the k value on top of

the base is used to determine the modulus of soil reaction on top of the base. The plate-bearing test

may be run on top of the base, or figure 2-1 may be used to determine the modulus of soil reaction on

top of the base. It is good practice to confirm adequacy of the k on top of the base from figure 2-1 by

running a field plate-load test.


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3. RIGID PAVEMENT BASECOURSES

3.1 General Requirements Base courses may be required under rigid pavements for replacing soft, highly compressible or

expansive soils and for providing the following:

Additional structural strength.

More uniform bearing surface for the pavement.

Protection for the subgrade against detrimental frost action.

Drainage.

Suitable surface for the oper ation of construction equipment, especially slipform pavers.
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Figure 3-1Design Curves for Plain Concrete Streets and Roads, and RCC

Figure 3-2Design Curves for Plain Concrete Parking and Storage Areas

Use of base courses under a rigid pavement to provide structural benefit should be based on economy

of construction. The first cost is usually less for an increase in thickness than for providing a thick base

course. However, thick base courses have often resulted in lower maintenance costs since the thickbase course provides stronger foundation and therefore less slab movement. A minimum basecourse

thickness of 4 inches is required over subgrades that are classified as OH, CH, CL, MH, ML, and OL to

provide protection against pumping. In certain cases of adverse moisture conditions (high water table

or poor drainage), SM and SC soils also may require base courses to prevent pumping. The designer is

cautioned against the use of fine-grained material for leveling courses or choking open-graded base

courses since this may create a pumping condition. Positive drainage should be provided for all base
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courses to ensure water is not trapped directly beneath the pavement since saturation of these layers

will cause the pumping condition that the base course is intended to prevent.

3.2 Materials If conditions indicate that a base course is desirable under a rigid pavement, a thorough investigation

should be made to determine the source, quantity, and characteristics of the available materials. A

study should also be made to determine the most economical thickness of material for a base course

that will meet the requirements. The base course may consist of natural, processed, or stabilized

materials. The material selected should be the one that best accomplishes the intended purpose of the

base course. In general, the basecourse material should be a well graded, high-stability material. In

this connection all base courses to be placed beneath concrete pavements for military roads and

streets should conform to the following

requirements:

Percent passing No.10 sieve; Not more than 85.

Percent passing No.200 sieve: Not more than 15. Plasticity index: Not higher than 6.

Where local experience indicates their desirability, other control limitations such as limited abrasion

loss may be imposed to ensure a uniform high quality base course.

3.3 Compaction Where base courses are used under rigid pavements, the basecourse material should be compacted to

a minimum of 95 percent of the maximum density. The engineer is cautioned that it is difficult to

compact thin base courses to high densities when they are placed on yielding subgrades.

3.4 Frost Requirements In areas where subgrade soils are subjected to seasonal frost action detrimental to the performance of

pavements, the requirements for basecourse thickness and gradation will follow the criteria in this

discussion.

4. CONCRETE PAVEMENT

4.1 Mix Proportioning and Control Normally, a design flexural strength at 28-day age will be used for the pavement thicknessdetermination. Should it be necessary to use the pavements at an earlier age, consideration should be

given to the use of a design flexural strength at the earlier age or to the use of high early strength

cement, whichever is more Mix proportion or pavement thickness may have to economical. Flyash

gains strength more slowly than cement, so that if used it may be desirable to select a strength value

at a period other than 28 days if time permits.


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4.2 Testing The flexural strength of the concrete and lean concrete base will be determined in accordance with

ASTM C 78. The standard test specimen will be a 6- by 6-inch section long enough to permit testing

over a span of 18 inches. The standard beam will be used for concrete with the maximum size

aggregate up to 2 inches. When

aggregate larger than the 2-inch nominal size is used in the concrete, the cross sectional dimensions

of the beam will be at least three times the nominal maximum size of the aggregate, and the length

will be increased to at least 2 inches more than three times the depth.

4.3 Special Conditions Mix proportion or pavement thickness may have to be adjusted due to results of concrete tests. If the

tests show a strength gain less than predicted or retrogression in strength, then the pavement would

have to be thicker. If the concrete strength was higher than predicted, then the thickness may be

reduced. Rather than modifying the thickness required as a result of tests on the concrete, the mix

proportioning could be changed to increase or decrease the concrete strength, thereby not changing

the thickness.

5. PLAIN CONCRETE PAVEMENTDESIGN

5.1 Roller-Compacted Concrete Pavements Roller-compacted concrete pavements (RCCP) are plain concrete pavements constructed using a zero-

slump portland cement concrete mixture that is placed with an AC paving machine and compacted

with

vibratory and rubber-tired rollers.

5.2 Design Procedure For convenience in determining design requirements, the entire range of vehicle loadings and traffic

intensities anticipated during the design life of pavements for the various classifications of roads and

streets has been expressed as an equivalent number of repetitions of an 18,000- pound single-axle

loading. To further simplify the design procedure, the range of equivalent repetitions of the basic

loading thus determined has been designated by a numerical scale defined as the pavement designindex. This index extends from 1 through 10 with an increase in numerical value indicative of an

increase in pavement design requirements. Values for the design index are determined using standard

procedures. Once the design index has been determined the required thickness of plain concrete

pavement is then obtained from the design chart presented in figure 5-1 for roads and streets. Figure

5-2 is used to determine the thickness of parking and storage areas except that the thickness of

rollercompacted concrete parking and storage areas will be designed using figure 5-1. These

design charts are graphical representations of the interrelation of flexural strength, modulus of


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subgrade reaction k, pavement thickness, and repetitions (design index) of the basic 18,000-pound

single-axle loading. These design charts are based on the theoretical analyses supplemented by

empirical modifications determined from accelerated traffic tests and observations of pavement

behavior under actual service conditions. The design charts are entered using the 28-day flexural

strength of the concrete.A horizontal projection is then made to the right to the design value for k. A

vertical projection is then made to the appropriate design-index line. A second horizontal projection tothe right is then made to intersect the scale of pavement thickness. The dashed line shown on curves

is an example of the correct use of the curves. When the thickness from the design curve indicates a

fractional value, it will be rounded up to the next -inch thickness. All plain concrete pavements will

be uniform in cross-sectional thickness. Thickened edges are not normally required since the design is

for free edge stresses. The minimum thickness of plain concrete for any military road, street, or open

storage area will be 6 inches.

6. REINFORCED CONCRETE

PAVEMENT DESIGN

6.1 Application Under certain conditions, concrete pavement slabs may be reinforced with welded wire fabric or

formed bar mats arranged in a square or rectangular grid. The advantages of using steel

reinforcement include a reduction in the required slab thickness, greater spacing between joints, and

reduced differential settlement due to nonuniform support or frost heave.

6.1.1 Subgrade conditions Reinforcement may reduce the damage resulting from cracked slabs. Cracking may occur in rigidpavements founded on subgrades where differential vertical movement is a definite potential. An

example is a foundation with definite or borderline frost susceptibility that cannot feasibly be made to

conform to conventional frost design requirements.

6.1.2 Economic considerations In general, reinforced concrete pavements will not be economically competitive with plain concrete

pavements of equal load-carrying capacity, even though a reduction in pavement thickness is possible.

Alternate bids, however, should be invited if reasonable doubt exists on this point.

6.1.2.1 Plain concrete pavements In otherwise plain concrete pavements, steel reinforcement should be used for the following

conditions:

Odd -shaped slabs. Odd-shaped slabs should be reinforced in two directions normal to each other

using a minimum of 0.05 percent of steel in both directions. The entire area of the slab should be

reinforced. An odd-shaped slab is considered to be one in which the longer dimension exceeds the


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shorter dimension by more than 25 percent or a slab which essentially is neither square nor

rectangular. Figure 6-1 includes examples of reinforcement required in oddshaped slabs.

Figure 6-1Typical Layout of Joints at Intersection

Mismatched joints. A partial reinforcement or slab is required where the joint patterns of abutting

pavements or adjacent paving lanes do Dot match, unless the pavements are positively separated by
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an expansion joint or slip-type joint having less than -inch bond-breaking medium. The pavement

slab directly opposite the mismatched joint should be reinforced with a minimum of 0.05 percent of

steel in directions normal to each other for a distance of 3 feet back from the juncture and for the full

width or length of the slab in 8 direction normal to the mismatched joint. Mismatched joints normally

will occur at intersections of pavements or between pavement and fil let areas as shown in figure 6-1.

6.2 Design Procedure 6.2.1 Thickness design on unbound base orsubbase

Figure 6-2Reinforced Rigid Pavement Design
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The design procedure for reinforced concrete pavements uses the principle of allowing a reduction in

the required thickness of plain concrete pavement due to the presence of the steel reinforcing. The

design procedure has been developed empirically from a limited Dumber of prototype test pavements

subjected to accelerated traffic testing. Although some cracking will occur in the pavement under the

design traffic loadings, the steel reinforcing will hold the cracks tightly closed. The reinforcing will

prevent spalling or faulting at the cracks and provide a serviceable pavement during the anticipateddesign life. Essentially, the design method consists of determining the percentage of steel required,

the thickness of reinforced concrete pavement, and the minimum allowable length of the slabs. Figure

6-2 presents a graphic solution for the design of reinforced concrete pavements. Since the thickness

of a reinforced concrete pavement is a function of the percentage of steel reinforcing, the designer

may determine either the required percentage of steel for a predetermined thickness of pavement or

the required thickness of pavement for a predetermined percentage of steel. In either case, it is

necessary to determine the required thickness of plain concrete pavement by the method outlined.

The plain concrete thickness h (to the nearest 0.1 inch) is used to enter the nomograph in Figure 6-2.

A straight line is then drawn from the value of hd to the value selected for either the reinforced

concrete thickness hr or the percentage of reinforcing steel S. It should be noted that the S value

indicated by figure 6-2 is the percentage to be used in the longitudinal direction only. For normal

designs, the percentage of steel

used in the transverse direction will be one- half of that to be used in the longitudinal direction. In

fillets, the percent steel will be the same in both directions. Once the h and S values have been

determined, the maximum allowable slab length L is obtained from the intersection of the straight line

and the scale for L. Difficulties may be encountered in sealing joints between very long slabs because

of volumetric changes caused by temperature changes.

6.2.2 Thickness design on stabilized base or

subgrade To determine the thickness requirements for reinforced concrete pavement on a stabilized foundation,it is first

necessary to determine the thickness of plain concrete pavement required over the stabilized layer

using procedures set forth above. This thickness of plain concrete is then used with figure 6-2 to

design the reinforced in the same manner discussed above for nonstabilized foundations.

6.3 Limitations The design criteria for reinforced concrete pavement for roads and streets may be subject to the

following limitations.

No reduction in the required thickness of plain concrete pavement should be allowed for percentages

of longitudinal steel less than 0.05 percent.

No further reduction in the required thickness of plain concrete pavement should be allowed over

that indicated in figure 6-2 for 0.5 percent longitudinal steel, regardless of the percentage of steel

used.


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The maximum length L of reinforced concrete pavement slabs should not excee d 75 feet regardless

of the percentage of longitudinal steel, yield strength of the steel, or thickness of the pavement. When

long slabs are used, special consideration must be given to joint design and sealant requirements.

Figure 6-3 (Part 1)Design Details of Reinforced Rigid Pavement with Two Traffic Lanes
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Figure 6-3 (Part 2)Design Details of Reinforced Rigid Pavement with Two Traffic Lanes

The minimum thickness of reinforced concrete pavements should be 6 inches, except that the

minimum thickness for driveways will be 5 inches and the minimum thickness for reinforced overlays

over rigid pavements will be 4 inches.

6.4 Reinforcing Steel 6.4.1 Type of reinforcing steel
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The reinforcing steel may be either deformed bars or welded wire fabric. Deformed bars should

conform to the requirements of ASTM A 615, A 616, or A 617. In general, grade 60 deformed bars

should be specified, but other grades may be used if warranted. Fabricated steel bar mats should

conform to ASTM A

184. Cold drawn wire for fabric reinforcement should conform to the requirements of requirements of

ASTM A 82, and welded steel wire fabric to ASTM A 185. The use of epoxy coated steel may beconsidered in areas where corrosion of the steel may be a problem.

6.4.2 Placement of reinforcing steel The reinforcing steel will be placed at a depth of hd + 1 inch from the surface of the reinforced slab.

This will place the steel above the neutral axis of the slab and will allow clearance for dowel bars. The

wire or bar sizes and spacing should be selected to give, as nearly as possible, the required

percentage of steel per foot of pavement width or length. In no case should the percent steel used be

less than that required by figure 6-2. Two layers of wire fabric or bar mat, one placed directly on top

of the other, may be used to obtain the required percent of steel; however, this should only be done

when it is impracticable to provide the required steel in one layer. If two layers of steel are used, thelayers must be fastened together (either wired or clipped) to prevent excessive separation during

concrete placement. When the reinforcement is installed and concrete is to be placed through the mat

or fabric, the minimum clear spacing between bars or wires will be 1 times the maximum size of

aggregate. If the strike-off method is used to place the reinforcement (layer of concrete placed and

struck off at the desired depth, the reinforcement placed on the plastic concrete, and the remaining

concrete placed on top of the reinforcement), the minimum spacing of wires or bars will not be less

than the maximum size of aggregate. Maximum bar or wire spacing or slab thickness shall not exceed

12 inches. The bar mat or wire fabric will be securely anchored to prevent forward creep of the steel

mats during concrete placement and finishing operations. The reinforcement shall be fabricated and

placed in such a manner that the spacing between the longitudinal wire or bar and the longitudinal

joint, or between the transverse wire or bar and the transverse joint, will not exceed 3 inches or one-

half of the wire or bar spacing in the fabric or mat.

The wires or bars will be lapped as follows:

Deformed steel bars will be overlapped for a distance of at least 24 bar diameters measured from

the tip of one bar to the tip of the other bar. The lapped bars will be wired or otherwise securely

fastened to prevent separation during concrete placement.

Wire fabric will be overlapped for a distance equal to at least one spacing of the wire in the fabric or

32 wire diameters, whichever is greater. The length of lap is measured from the tip of one wire to the

tip of the other wire normal to the lap. The wires in the lap will be wired or otherwise securelyfastened to prevent separation during concrete placement.


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Figure 6-4Design Details of Reinforced Rigid Pavement with Traffic and Parking

Lanes
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CIVIL ENGINEERING BASIC QUESTIONS

What are the steps involved in the concreting process, explain? The major steps involved in the process of concreting are as follows:1. Batching2. Mixing3. Transporting and placing of concrete4. Compacting.

> Batching: The process of measurement of the different materials for the makingof concrete is known as batching. batching is usually done in two ways: volume

batching and weight batching. In case of volume batching the measurement is donein the form of volume whereas in the case of weight batching it is done by the

weight.> Mixing: In order to create good concrete the mixing of the materials should befirst done in dry condition and after it wet condition. The two general methods ofmixing are: hand mixing and machine mixing.> Transportation and placing of concrete: Once the concrete mixture is createdit must be transported to its final location. The concrete is placed on form worksand should always be dropped on its final location as closely as possible.> Compaction of concrete: When concrete is placed it can have air bubblesentrapped in it which can lead to the reduction of the strength by 30%. In order toreduce the air bubbles the process of compaction is performed. Compaction isgenerally performed in two ways: by hand or by the use of vibrators. Describe briefly the various methods of concrete curing. Curing is the process of maintaining the moisture and temperature conditions forfreshly deployed concrete. This is done for small duration of time to allow thehardening of concrete. The methods that are involved in saving the shrinkage ofthe concrete includes:(a) Spraying of water: on walls, and columns can be cured by sprinkling water.(b) Wet covering of surface: can be cured by using the surface with wet gunny

bags or straw

(c) Ponding: the horizontal surfaces including the slab and floors can be cured bystagnating the water.(d) Steam curing: of pre-fabricated concrete units steam can be cured by passingit over the units that are under closed chambers. It allows faster curing process andresults in faster recovery.(e) Application of curing compounds: compounds having calcium chloride can

be applied on curing surface. This keeps the surface wet for a very long time.


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What do you understand by preset during the installation process of bridgebearings? During the installation of bridge bearings the size of the upper plates is reduced tosave the material costs. This process is known as preset. Generally the upper

bearing plate comprises of the following components:> Length of bearing> 2 x irreversible movement.> 2 x reversible movement.The bearing initially is placed right in the middle point of the upper bearing plate.

No directional effects of irreversible movement is considered. But since theirreversible movement usually takes place in one direction only the displaceddirection is placed away from the midpoint. In such cases the length of the upper

plate is equal to the length of the length of the bearing + irreversible movement + 2x reversible movement.

Why are steel plates inserted inside bearings in elastomeric bearings? In order to make a elastomeric bearing act/ function as a soft spring it should bemade to allow it to bulge laterally and also the stiffness compression can beincreased by simply increasing the limiting amount of the lateral bulging. In manycases in order to increase the compression stiffness of the bearing the usage ofmetal plates is made. Once steel plates are included in the bearings the freedom ofthe bulge is restricted dramatically, also the deflection of the bearing is reduced ascompared to a bearing without the presence of steel plates. The tensile stresses ofthe bearings are induced into the steel plates. But the presence of the metal platesdoes not affect the shear stiffness of the bearings. What reinforcements are used in the process of prestressing? The major types of reinforcements used in prestressing are:> Spalling Reinforcement: The spalling stresses leads to stress behind the loadedarea of the anchor blocks. This results in the breaking off of the surface concrete.The most likely causes of such types of stresses are Poisson`s effects straininteroperability or by the stress trajectory shapes.> Equilibrium reinforcements: This type of reinforcements are required whereseveral anchorages exist where the prestressing loads are applied in a sequentialmanner.

> Bursting Reinforcements: These kinds of stresses occur in cases where thestress trajectories are concave towards the line of action of load. In order to reducesuch stresses reinforcements in the form of bursting is required.

6. In the design of bridge arguments what considerations should be made to select

the orientation of the wing walls?


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Some of the most common arrangements of wing walls in cases of bridgearguments are as follows:> Wing walls parallel to abutments: This method is considered to take leastamount of time to build and is simple as well. But on the downside this method isnot the most economical. The advantage of this type of design being that theycause the least amount of disturbance to the slope embankment.> Wing walls at an angle to abutments: This design method is considered to bethe most economical in terms of material cost.> Wing walls perpendicular to abutments: The characteristic of this design is it

provides an alignment continuous with the bridge decks lending a support to the parapets.

7. In case if concrete box girder bridges how is the number of cells determined? When the depth of a box girder bridge exceed 1/6th or 1/5th of the bridge width

then the design recommended is that of a single cell box girder bridge. But in casethe depth of the bridge is lower than 1/6th of the bridge width then a twin-cell or insome cases multiple cell is the preferred choice. One should also note that even inthe cases of wider bridges where there depths are comparatively low the number ofcells should be minimized. This is so as there is noticeably not much improvementin the transverse load distribution when the number of cells of the box girder ishigher than three or more.

8. Under what circumstances should pot bearings be used instead of elastomeric

bearings? Pot bearings are preferred over elastomeric bearings in situations where there arechances of high vertical loads in combinations of very large angle of rotations.Elastomeric bearings always require a large bearing surface so that a compressionis maintained between the contact surfaces in between the piers and the bearings.This is not possible to maintained in high load and rotation environment. Also theusage of elastomeric bearings leads to the uneven distribution of stress on the piers.This results in some highly induced stresses to be targeted at the piers henceforthdamaging them. Due to the above reasons pot bearings are preferred over

elastomeric bearings in such cases.

9. Why should pumping be not used in case of concreting works? During the pumping operation the pump exerted pressure must overcome anyfriction between the pumping pipes and the concrete, also the weight of theconcrete and the pressure head when the concrete is placed above the pumps. Sinceonly water is pump able, all the pressure generated is by the water that is present in


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the concrete. The major problem due to pumping are segregation effects and bleeding. In order to rectify and reduce these effects, generally the proportion ofthe cement is increased in order to increase the cohesion , which leads to thereduction of segregation and bleeding. Also if a proper selection of the aggregategrading can vastly improve the concrete pump ability.

10. Why should curing not be done by ponding and polythene sheets? The primary purpose of curing is to reduce the heat loss of concrete that is freshly

placed to the atmosphere and in order to reduce the temperature gradient across thecross-section of the concrete. Ponding is not preferred for curing as this method ofthermal curing is greatly affected by cold winds. In addition to that in pondinglarge amounts of water is used and has to be disposed off from the constructionsites. Polythene sheets are used on the basis that it creates an airtight environmentaround the concrete surface henceforth reducing the chances of evaporation over

fresh concrete surfaces. But the usage of polythene can be a drawback as it can beeasily blown away by winds and also the water lost by self-desiccation cannot bereplenished.

11. What are the different type of slump test indications? Slump tests are performed to empirically measure the workability of freshconcrete. It is used to measure the consistency of the concrete. In general there arethree different types of slumps that occur in slump tests. They are as follows:> True Slump> Shear Slump> Collapse Slump

True Slump: This type of slump is characterized by the general drop of theconcrete mass evenly without visible signs of deterioration or disintegration. Shear Slump: It indicates that the concrete mix is deficient in cohesion. This typeof slump leads to segregation and bleeding. Henceforth in the long run effectingthe durability of the concrete. Collapse Slump: This type of slump is indicates that the mix of concrete is simplytoo wet. The mix is considered to be harsh and lean.

12. Why is propping required for long structures once the formwork is removed? Once the process of concreting is performed the striking of the formworks should

be done as soon as possible as delay in this process can lead to the discoloration ofthe concrete structures. In case of long structures particularly long span structuresonce the structures have attained enough strength to support themselves it isessential to provide them with propping as creep deflection can take place which


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can greatly reduce the integrity of the structure. Due to the above mentionedreasons propping should be done after the removal of formwork. Also the propsshould not be made to stand long as it can lead to overstress for the structures.

13. Explain the mechanism of cavitations in pipes and drains? The formation of air bubbles in a fluid due to low pressure conditions lower thanthe saturation pressure is known as cavitations. This is considered to be a high

potential damage condition where the strength and durability of the pipes can begreatly reduced. Cavitation works on the principle of Bernoulli's Equation. Whenfluids are at high velocities the pressure head of fluids reduce accordingly. Butsince the fluid pressure is lower than the saturation pressure the dissolved gases getreleased from the flowing fluid. These air bubbles suddenly collapse on entering aregion of high pressure. This leads to the damage of the pipelines as a high level ofdynamic pressure is created.

14. For what purpose bedding is used under storm water drains, explain? Beddings are primarily made up of granular or concrete materials. They are

primarily used for the following purposes:> They are used to provide a more uniform support for the under pipes so that the

bending moment longitudinally can be reduced greatly. > In order to enable the pipes to get more load-supporting strength.> They are also used to act as a platform to achieve a more correct alignment andlevel pre and post construction.> In case of pipes which contain spigot and socket joints, it enables pipes to getsupported along pipe lengths in place of sockets. Otherwise it can lead to unevenstress being induced on the pipes eventually damaging it.

15. Why are pull-out tests performed for soil nails? Pull out tests are performed for primarily the following reasons:> In order to detect and the verification of the bond strength among the soil and thegrout adopted during the design of soil nails. This is considered to be as the

primary objective of performing pull out tests for soil nails.> For the detection of any slippage or occurrence of creeps.

> To detect the elastic and deformations (plastic) of any of the test nails employed.Observations are made during the loading and unloading cycles of the soil nailsrepetitively.> To achieve the perfect balance the test nails should always be loaded so that theultimate soil/grout mixture with an upper limit of 80%.


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16. Describe briefly the advantages and disadvantages of using plastic and timber

fenders? The advantages and disadvantages of using plastic fenders are as follows:Plastic fenders are low in strength with a relatively high resistance to abrasion.Plastic fenders are resistant to chemical and biological attacks. Plastic fenders havemoderate energy absorption capacity. The berthing reactions are alsocomparatively moderate and depends on the point of contact. Also since they aremade from recycled material they are environmental friendly.The advantages and disadvantages of using timber fenders are:timber fenders are low in strength and are very susceptible to marine borer attacksand rotting. The energy absorption capacity is very low. Also generally the contact

pressure between the vessels and the fender are high.

17. Explain why concrete barriers have curved surface profiles? The concrete safety fencings are made to contain vehicles in their carriageway

being travelled so as to reduce the chances of rebounding into the roads leading tomore hazards. In the case of normal fencings upon vehicle crashes the fencingsgive away so as to absorb as much energy as possible henceforth reducing theimpact on the vehicles. But in the case of concrete barriers their purpose is not toabsorb energy of vehicles crashing into the barrier but to retain them. They have acurved design so as to allow the vehicles that hit them to slightly go up on the

barrier but not overturn. They also prevent the vehicle from again getting back onthe road by rebounds. This helps in vastly reducing the chances of other vehiclehazards.

18. Why is the use of granular sub-base in concrete carriageways not preferred,

explain? Some of the reasons why granular sub-base is not preferred in concretecarriageways:> Sub bases are permeable and hence water can seep through them easily. The soil

particles get pumped out through the joints on the application of traffic loads. Thisresults in the creation of voids underneath the pavement structure. This leads to theweakening of the concrete surface and it can crack easily upon intense trafficloads.> Instead if lean concrete is used for carriageways it greatly increases the strengthof the roads and the load carrying capacity of the roads is increased.> Sub-bases implementation requires a lot of workmanship which can lead to an


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un-uniform distribution of the sub-base. This can lead to the cracking of thecarriageway when there is severe traffic loading.

19. Why are separation membranes used between concrete pavement slab and sub-

base? The purpose of separation membrane between the concrete pavement slab and thesub-base are as follows:> The separation membrane reduces the frictional forces between the concreteslabs and the sub-base. The membrane aids the movement of the concrete slab inreference to the sub-base when changes in the level of the moisture andtemperature occurs.> It aids in the segregation of sub-base materials from freshly placed concrete.> The separation membrane also helps in the reduction of cement and water loss in

the form of immature concrete. Immature concrete greatly affects the strength ofthe concrete. It also affects the durability of it. A good example of a separation membranes is polythene sheeting which iscommonly used.

20. In the roof of a pumping station explain briefly the components of a

waterproofing system. The components of a typical waterproofing system on the roof of a pumpingstation are as follows:> Right above the structural finish level of the roof ( concrete ) a uniform thicknessscreed is applied so as to facilitate the application of the waterproofing membrane.The surface provide for the membrane should always possess good cohesion

properties and must be thin so as to prevent any un-uniformity. This thin layer alsoacts as a layer of thermal insulation.> Right above this layer the waterproofing membrane is deployed to secure thewater tightness of the roof.> In order to enhance the thermal insulation of the roof an insulation board issometime placed right above the waterproof membrane. The insulation board helps

in the maintenance of a stable temperature in both weathers.

21. During reclamation how can the occurrence of mud waves can be rectified? There are several solution to the rectification of the problem of mud waves:> Complete removal of all the disturbed mud: This method can be considered to beone of the fastest methods. As soon as the disturbed mud is removed some fillingmaterial is used to replace the disturbed mud. But economically this method can be


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expensive as compared to others.> Accelerated consolidation of disturbed mud: In this method surcharging loads are

placed on top of the mud waves. Along with this band drains are installed toaccelerate the consolidation process. This method is quite slow compared to theother methods.> Partial removal of the disturbed mud: This method is the hybrid of the above twomethods where the top layer is removed whereas the lower level is treated with thesurcharging process.

22. In reclamation works what are the importance of geotextiles and sand? The primary purposes of geotextiles and sand in reclamation works are as follows:> Geotextiles: They are used to separate the marine mud from the reclamation fill.Also geotextiles are used as reinforcements in reclamation processes to increase itsstability. It is still debated as to whether the usage of geotextiles is better or are the

old processes followed are better as the performance has not been comparable tothe conventional methods.> Sand: In reclamation process sand is used to spread the load of any future publicdumps placed on top of it. Sand also acts as a drainage for the excess pore water

pressure of band drain installations.

23. In block work seawalls what is the purpose of slip joints? Joints which are formed from the cope level to the toe level of seawalls through acomplete vertical plane are known as slip joints. Such joints are designed so as tohandle the differential settlements between the seawalls adjacent panels. In the slip

joints the aggregates inside the half-rounds channels enables some verticalmovements. These vertical movements are induced by differential settlements.This enables in the interlocking of the adjacent panels of the seawalls to link the

panels in one unit against the earth pressure ( lateral ) which is exerted on theseawalls.

24. For a washout valve why are two gate valves required in normal practice? The washout valves are primarily used for normal maintenance works such as thatof water main. This can be like to allow water to flow out during the cleaning of

the water main. The junctions at which a pipe branches out to a washout pointusually a gate valve is installed so that the two pipelines are separated. The gatevalve installed above usually remains open during normal operation. Another gatevalve is installed further downstream and this remains closed during normaloperation of the washout valve. In case this valve is not installed then the pipesection of the branched out pipe would remain dry during normal operation andhigh chances of damage and leakage can take place. When the downstream valve is


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installed the branched out water main contains water under normal operation. Withtwo gate valves installed a leakage can be detected immediately.

25. What are the different approaches in designing the floors of the service

reservoirs? In general there are two main approaches of designing the reservoir floors to prevent leakage of water due to seasonal and shrinkage movements:> In this approach the movement joints of the reservoir floor panels are such thatthe free expansion and contraction of the panels takes place. Every panel is isolatedfrom the other panels and two panels have a sliding layer between them to help insliding.> The second method does not provide any room for free movement. Withseasonal and shrinkage movements, some cracks are designed to voluntarily occur

on the floors of the service reservoirs. These tiny cracks are spread throughout thefloor and are simply too minute to cause any leakage or corrosion of the floors. Butthe difference also in this method is that the amount of reinforcement used is muchmore than the first approach

1. INTRODUCTION 1.1 Importance of Building Energy Efficiency

Buildings are significant users of energy and building energy efficiency is a high priority in many countries.

Efficient use of energy is important since global energy resources is finite and power generation using fossil fuels (suchas coal and oil) has adverse environmental effects.

The potential for energy savings in the building sector is large.

1.2 Assumption

Energy efficient building design is location-dependent. The local climate must be considered when selectingappropriate design strategies.

A cooling-dominated climate is assumed here. However, some of the general principles are also applicable to otherclimate types.

2. BASIC PRINCIPLES 2.1 Climate and Site

Climate has a major effect on building performance and energy consumption. Energy-conscious design requires anunderstanding of the climate.

Buildings will respond to the natural climatic environment in two ways:


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o Thermal response of the building structure (heat transfer and thermal storage).o Response of the bui ldi ng systems (such as HVAC and lighting systems).

To gain the maximum benefits from the local climate, building design must "fit" its particular climate. When faced with unfavorable climatic conditions, optimal siting and site design may solve all or part of the problems.

Site elements to be considered include:o Topography - slopes, valleys, hills and their surface conditions.o Vegetation - plant types, mass, texture.o Built forms - surrounding buildings and structures.o Water - cooling effects, ground water, aquifers.

The six important aspects of architectural planning which will affect thermal and energy performance of buildings are:o Site selectiono Layouto Shapeo Spacingo Orientationo Mutual relationship

Architectural and landscape designs should be closely integrated. If possible, should provide wind breaks in cold winterand access to cooling breezes in summer.

Wind control in site analysis

2.2 Building Envelope

Elements of the building envelope (= "protective skin"):o Walls (exterior)o Windows o Roof o Underground slab and foundation

Three factors determining the heat flow across the building envelope:o Temperature differentialo Area of the building exposedo Heat transmission value of the exposed area

The use of suitable thermal mass and thermal insulation is important for controlling the heat flow. Remember, theenvelope components will respond "dynamically" to changing ambient conditions.

Some people also consider the " embodied energy " (include energy for producing and transporting) of buildingmaterials when making the selection.
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Building envelope design that combines passive solar, daylighting and organic horticulture

2.3 Building Systems

H eating, venti lation and air -conditionin g (H VAC) systems are installed to provide for occupant comfort, health andsafety. They are usually the key energy users and their design is affected by architecture features and occupant needs.

While being energy efficient, HVAC systems should have a degree of flexibility to allow for future extensions andchange.

To achieve optimum energy efficiency, designers should evaluate:o Thermal comfor t cri teri a o Load calculation methods o System characteri stics o Equi pment and pl ant operation (part-load)

Lighting systems is another key energy user and additional cooling energy will be required to remove the heatgenerated by luminaires.

Energy efficient lighting should ensure that:o Illumination is not excessive.o Switching is provided to turn off unnecessary light.o Illumination is provided in an efficient manner.

General design strategies for lighting design:o Combination of general and task lighting.o Electric lighting integrated with daylight.o The use of energy efficient lamps and luminaires.o Use light-coloured room surfaces.

Other bui ldi ng servi ces systems consuming energy include: Electrical installations Lifts and escalators Water supply systems Town gas supply system

3. TECHNOLOGIES 3.1 Passive Cooling and Sun Control
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Passive systems - internal conditions are modified as a result of the behavior of the building form and fabric.

General strategies for passive heating and cooling:

o Cold winters - maximize solar gain and reduce heat loss.o Hot summers - minimize solar gain and maximize heat removal.o Correct orientation and use of windows.o Appropriate amounts of thermal mass and insulation.o Provision for ventilation (natural).

Strategies for shading and sun contr ol :

o External proj ection (overhangs and side fins).o External systems integral with the window frame or attached to the building face, such as louvers and

screens.o Special ly tr eated win dow glass , such as heat absorbing and reflecting glass.o I nternal tr eatments either opaque or semi-opaque, such as curtains and blinds.

For hot and humid climate, extensive shading without affecting ventilation is usually required all year round. Shadingof the east and west facades is more important.

3.2 Daylighting

Daylight can be used to augment or replace electric lighting. Efficient daylighting design should consider:

o Sky conditionso Site environmento Building space and formo Glazing systemso Artificial lighting systemso Air-conditioning systems

The complex interaction between daylight, electric lights and HVAC should be studied carefully in order to achieve adesirable solution.

Day lighting design in an atrium
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Advanced window technologies have been developed to change/switch the optical properties of window glass so as tocontrol the amount of daylight. There are also innovative day lighting technologies now being investigated:

o Light pipe systemso Light shelveso Mirror systemso Prismatic glazingo Holographic diffracting systems

3.3 HVAC Systems

Energy efficiency of many HVAC sub-systems and equipment has been improved gradually over the years, such as inair systems, water systems, central cooling and heating plants.

Energy efficient HVAC design now being used or studied include:

o Variable air volume (VAV) systems to reduce fan energy use.o Outside air control by temperature/enthalpy level.o Heat pump and heat recovery systemso Building energy management and control systems.o Natural ventilation and natural cooling strategies.

Schematic of a typical solar hot water system

Th ermal storage systems (such as ice thermal storage) are also being studied to achieve energy cost saving. Althoughin principle they will not increase energy efficiency, they are useful for demand-side management.

3.4 Active Solar and Photovoltaics

Solar thermal systems (active solar) provide useful heat at a low temperature. This technology is mature and can beapplied to hot water, space heating, swimming pool heating and space absorption cooling.

The system consists of solar collectors, a heat storage tank and water distribution mains. An integrated collector storagesystem has also been developed recently to eliminate the need for a separate storage tank.
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Photovoltai c (PV) systems convert sunlight into electricity using a semi-conductor device. The main advantages of PVsystems include:

o Reasonable conversion efficiencies (6-18%).o PV modules can be efficiently integrated in buildings, minimising visual intrusion.o Their modularity and static character.o High reliability and long lifetime.o Low maintenance cost.

In practice, PV technology can be used for central generation or building-integrated systems (BIPV). The systems can be of the standalone type, hybrid type or grid-connected type. Although the cost of PV is still high at present, it may become cost-effective in the hear future.

Grid-connected solar photovoltaic system

4. EVALUATION METHODS 4.1 Bioclimatic Design

The integration of design, cl imate and human comfor t -- the bioclimatic approach to architectural regionalism -- wasfirst proposed in mide-1950s by Victor and Aladar Olgyay .

Their intention was to highlight the belief that architectural design should begin with understanding of the physiological needs of human comfort and take advantage of local climatic elements to optimize these requirementsnaturally and efficiently.

Building design itself is conceived as natural energy systems that restores environmental quality to its site.

The aim is to create a supportive and productive environment that ultimately can contribute to sustaining the regionaland global environment.

4.2 Building Thermal and Energy Simulation

Nowadays, building energy design often require the analytical power to study complicated design scenario. Computer- based building energy simulation will provide this power and allow greater flexibility in design evaluation.

The simulation method is based upon load and energy calculations in HVAC design. The purpose is to study anddetermine the energy characteristics of buildings and their building systems.

The cost effectiveness of any energy conservation measures will be a compromise between initial, maintenance andenergy costs. Simulation techniques can provide the tools for assessing different design options based on their energy

performance and life cycle costs.
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4.3 Building Energy Audits

Building energy auditing can be defined as "measuring and recording actual energy consumption, at site, of acompleted and occupied building (expressed in units of energy, not monetary value); fundamentally for the purposes ofreducing and minimising energy usage".

Energy audits identify areas where energy is being used efficiently or is being wasted, and spotlight areas with thelargest potential for energy saving. They are useful for establishing consumption patterns, understanding how the

building consumes energy, how the system elements interrelate and how the external environment affects the building.

There are different approaches to conducting a full building energy audit, but the following stages are often adopted:o Stage 1 - An audit of hi stori cal data o Stage 2 - Survey o Stage 3 - Detail ed in vestigation an d analysis

A proper energy audit is useful for more than energy conservation goals. Energy audits can be employed to assist inareas such as:

o Establishment of data bank and consumption records.o Estimating of energy costs.o Determining of consumption patterns and utility rates.o Establishment of an operational overview.

5. CONCLUSIONS Building energy design challenges building designers to think about climate, orientation, day lighting, and the qualities

of environment as part of the initial design conception.

It also requires the architectural and engin eeri ng disciplin es to work as a team early in the design phase and toconceptualize the building as a system.

Architects and engineers who incorporate energy design concepts and methods into their design projects can play asignificant role in reducing energy consumption and achieving sustainable energy structure for our society.

Bonding fresh, plastic concrete to old, hardened concrete increases the strength of thecomposite material . Fresh patches, concrete adjacent to construction joints , and overlays all

benefit from bonding to the hardened concrete substrate. Bond is not, however, guaranteed.

It must be ensured through proper surface preparation, material choice and use, and curing.

Ignoring one of these components does not mean a one-third decrease in bond; it may result

in the total loss of bond.

Surface Preparation

All damaged, loosened, or unbonded portions of existing concrete should be removed bychipping hammers or other mechanical methods. Prepare the exposed concrete by wet

sandblasting, water blasting, or shot blasting. Then clean it and allow it to dry thoroughly. This

removes any laitance , soft mortar, dirt, wood chips, form oil, or other foreign materials that

may interfre with proper bonding of the new concrete.

Pressurized water and air is commonly used for surface preparation. Be sure that water usedin cleaning is itself clean and also that no contaminants are present in the compressed air. ACI

503 (Ref. 2) recommends that all equipment supplying compressed air be equipped with
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efficient oil and water traps to prevent surface contamination from the compressed air supply.

Acid etching was once considered another way to prepare a surface, but experience showsthat this method is not as dependable as mechanical methods ( ACI 503R). Also, some

cleaning acids contain chlorides that can start rebar corrosion. Acid etching is not

recommended unless no other means of cleaning is possible.

Patches

Patches are easier to make and more successful if they are made as soon as practical,

preferably when th e concrete is still green. Successful patches can be made, however, at any

time. The edges of the defective area should be chipped or cut straight and at right angles to

the surface, or slightly undercut to provide a key at the edge of the patch. Most contractors

saw cut around the defective material. This helps define the scope of work for the laborers and

provides a right angle surface cut.

Figure 1. The feathered edges of the top drawing will break down undertraffic or will weather off. The chipped area should be at least 34 inch

deep (see bottom drawing) with the edges at right angles or undercut tothe surface.

Whatever the method, no feather edges should be permitted ( Figure1 ). When chipping

around reinforcement leave at least a l-inch space around each exposed bar. Always leave

rebar partially embedded.
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Construction Joints Workers can prepare the surface of construction joints during the first concrete placement. For

horizontal construction joints , the top surface of fresh concrete can be roughened while still

plastic. Green concrete, 12 to 24 hours old, can be easily cut or wire brushed to create a

roughened surface.

Sometimes workers sprinkle or mix retarders into the top layer of concrete. Delaying the setallows the surface to be roughened up to 48 hours after the pour. For vertical

construction joints placed against bulkheads, the concrete surface is generally too smooth to

permit proper bonding. Stiff- wire brushing may be sufficient if the concrete is less than 3

days old. Otherwise bushhammering or sand or waterblasting may be needed. Follow this by

washing to remove all the dust and loose particles.

Overlays

For bonded two-course floors, the surface of the partially set base course is usually brushed

with a coarse wire broom to remove laitance and score the surface. Then it should be wet

cured for 3 days. Dont use curing compounds as they can interfere with bonding. If the slab is

being repaired with a bonded overlay, then techniques developed for the pavement industry

are typically appropriate. Bonding of two-course floors is difficult.

Without close attention to detail, the bond wont be successful. Slabs on grade and pavementsnow can be cleaned fast with high production, self-propelled cold milling equipment and

improved blasting techniques. The type of coarse aggregate in the existing pavement usually

dictates the least costly way to prepare a surface. Most agencies specify the surface cleaningmethod and minimum depth of surface removal. The US Army Corps of Engineers requires

removal of at least 1/4 inch from the surface by scarification followed by high-pressure water

flushing and air blowing. The Portland Cement Association (PCA) recommends that the surface

be scarified to remove unsound concrete and cleaned by sandblasting or other means.

Bonding Medium

The most practical and economical bonding agents are sand-cement and water-cement grouts.

Epoxy resin grouts specially formulated for each application also are on the market. ACI 503

details the use and specification of epoxies for bonding fresh to hardened concrete. Thebonding sand-cement grouts usually consist of 1 part cement, 1 part sand, and enough water

(about 1/2 part) to form a creamy consistency.

The sand should pass the No. 30 sieve. Proportion water- cement bonding grouts at the rate of

1 bag of cement to 6 to 7 gallons of water. Some project specifications permit a water-cement

grout with a water cement ratio of 0.62. This allows the grout to be sprayed on the surface to
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a depth of about 116 inch.

Epoxy resins and their hardeners or curing agents are co-reactants in a chemical reaction thatallows the material to harden. The proportioning of the resin and hardener is extremely

important; they must be mixed thoroughly to produce a homogenous mixture. This ensures a

complete reaction. Epoxy resins can be formulated for different temperatures and for dry ordamp surfaces.

The ability to be used on a damp surface is sometimes an advantage. Regardless of the

bonding medium, a minimum bond strength is required. Based on laboratory and field tests,

Felt (Ref. 4) concludes that bond strengths greater than 400 psi may be achieved, but that

strengths of 200 psi or less may be adequate. The bond strength of 200 psi is generally used

as a guide in designing bonding media.

Bonding Procedure After preparing the surface, the contractor need only decide if the concrete should be dry or

damp before brooming or brushing the bonding medium into place. Most agencies recommend

a damp surface free of water, especially in hot, windy weather. Protect the bonding medium

from drying above and below. Hot, windy weather dries the bonding medium from above.

From below, porous aggregates or concrete can absorb enough water to prevent complete

hydration. This produces a weak bond interface or the porous surface can absorb enough

epoxy to starve the glue line.

Apply the grout immediately before placing the new concrete . Place only as much grout as canbe covered with fresh concrete before the grout dries. The amount of grout varies with

weather, equipment, and crew. After applying the bonding medium, place the concrete as

usual.

Curing

Start curing as soon as possible after placing the fresh concrete. Use wet burlap, wet sand,

plastic sheets, curing paper, tarpaulins, curing compounds, or a combination. Moisture and

temperature both affect the curing of bonded concrete. Differential shrinkage, thermal

movements, or moisture gradients can cause enough stress to break the bond during the

curing period. This is especially important when the new concrete has different properties

(modulus of elasticity, coefficient of thermal expansion, shrinkage strains) than the underlying

concrete.
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AASHTO stands for American Association of State Highway

and Transportation Officials.AASHTO proposed soil classification in 1929 and had undergone

several revisions till now. It is widely used to classify soil fo r construction of roads, highways, and airfield (runways, taxiways)

especially for subgrade material. Pre-requisites of AASHTO soil classification system are: 1) Mechanical analysis 2) Liquid limit 3) Plasticity Index.

Grain Size: 1) Gravel: Fraction passing 75mm sieve and retained on #10 (2mm) US sieve 2) Sand: Fraction passing #10 sieve and retained #200 sieve 3) Silt and Clay: Fraction passing #200 sieve

Plasticity: 1) Term silty is applied when fine fractions have a PI < 10 2) Term clayey is applied when fine fractions have PI > 11 Note: If cobbles and boulders (larger than 75mm) are encountered, they are excluded from the

portion of the soil sample on which classification is made. However, %age of such material isrecorded.

Groups: Soils are classified into eight groups, A-1 through A-8.The major groups A-1, A-2, and a-3

represent the coarse grained soils and the A-4, A-5, A-6, and A-7 represent fine grained soils. A-8are identified by visual inspection. The ranges of the LL and PI for groups A-4, A-5 A-6 and A-7are shown in Fig.1.
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Figure 1 : Ranges of liquid limit and plasticity index for A-4, A-5, A-6 and A-7.

Group Index ( GI ) For qualitative evaluation of a given soil, a number referred as the Group Index has also been

developed. GI = ( F 200 -35 ) [ 0.2 + 0.005 ( LL-40) ] + 0.01 ( F 200 -15 ) ( PI 10) Where; F or F 200 is %age passing #200 sieves expressed as whole number (also called as fine fraction) LL is liquid limit of soil PI is Plasticity Index of soil

The higher the value of GI the weaker will be the soil and vice versa. Thus, quality of

performance of a soil as a subgrade material is inversely proportional to GI . A soil having GI

of zero is considered as the best. If equation gives negative value for GI, consider it zero.

Always round off the GI to nearest whole number.
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GI = 0 for soils of groups A-1-a, A-1-b, A-2-4, A-2-5, and A-3. For groups A-2-6 and A-2-7

use partial GI for PI only.

DESCRIPTION OF GROUPS & SUBGROUPS: Group A-1. The typical material of this group is a well-graded mixture of stone

fragments or gravels, coarse sand, fine sand, and a non-plastic or sligthly plastic soil binder. This group also includes stone fragments, gravels, coarse sand, volcanic cindersetc, without a well-graded binder of fine material.

Subgroup A-1-a includes those materials consisting predominantly of stonefragments or gravel, either with or without a well-graded binder of fine material.

Subgroup A-1-b includes those materials consisting predominantly of coarsesand with or without a well-graded soil binder.

Group A-3. The typical material of this group is fine beach sand or fine desert blown sand without silty or clayey fines or with a small amount of non-plastic silt. Thisgroup includes also stream-deposited mixtures of poorly graded fine sand and limitedamounts of coarse sand and gravel.

Group A-2 . This group includes a wide variety of granular materials, w hich areat the borderline between the materials falling in groups A-1 and A-3 and the silty-claymaterials of group A-4 through A-7. It include any materials not more than 35% of which

passes a #200 sieve and which cannot be classified as A-1 or A-3 because of having finescontent or plasticity, or both, in excess of the limitations for those groups.

Group A-4. The typical material of this group is a non-plastic or moderately plastic silty soil 75% or more of which usually passes the #200 sieve. The group alsoincludes mixture of fine silty soil and up to 64% of sand and gravel retained on the #200sieve.

Group A-5 .The typical material of this group is similar to that described underGroup A-4, but it may be highly elastic, as indicated by high liquid limit.

Group A-6 . The typical material of this group is a plastic clay soil 75% or moreof which usually passes the #200 sieve. The group also includes mixtures of fine clayeysoil and up to 64% of sand and gravel retained on the #200 sieve. Materials of this groupusually have high volume change between wet and dry states.

Group A-7 . The typical material of this group is similar to that described underGroup A-6, but it has the high liquid limits characteristics of the A-5 group and may beelastic as well as subject to high volume change.

Subgroup A-7-5 includes those materials which have moderate plasticityindexes in relation to liquid limit and which may be highly elastic as well as subject toconsiderable volume change.

Subgroup A-7-6 includes those materials which have high plasticity indexesin relation to liquid limit and which are subject to extremely high volume change.

Group A-8 . The typical material of this group is peat and muck soil ordinarilyfound in obviously unstable, swampy areas. Characterized by:

low density high compressibility high water content and high organic matter content.
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Table 1. Classification of Highways subgrade material
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an introduction to rigid pavement design

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